Safety lock for switches



Dec.

E. R. M KITRICK SAFETY LOCK FOR SWITCHES Filed Aug. 7, 1951 I N VEN TOR.

Edward I; gwzz Patented Dec. 15, 1953 "SAFETY LOCK FORSWITCHES Edward 'R. 'McKitrick, Detrit,:-Mich., assignor to Briggs Manufacturing Go..-, Detroit, Mich., a

corporation of. Michigan Iii-Claims.

1 This invention relates to-a safety: lock for electrical switches and-morerparticularly to aisafety lock for electrical switches use-dto-control the starting and stopping of theoperation of metal stamping presses or other -machines and apparatus.

One type of electrical switch commonly used to control the operation of. metal. stamping presses and. other machines or apparatuscomprises a housing which encloses the electrical contact elements of the switch and which provides aamounting for at least two actuators or push buttonzelementsfor shifting the contact'elements-to open and close the necessary electrical circuits for starting or stopping thedrive; means of thezpress orhmachine. In this type ofuswitchat leastaone of thebuttons must be. pressed to startith'e operation of the press or machine andtanother of the buttons must be pressed to stop :thexioperatiion thereof. The start an'dlstop buttons are interlocked, preferably by mechanical'm'eans.in -such amanner that movement of .one'buttoninwardly into arecessed position within the1housingeaiitomatically' results in the other button being moved outwardly to project beyond thesuriace of the housing in accessible position tozbefactuated-by the machine operator to -startor=tstopithe machine, as the case may be. For examplegwhen the press or machine is in operation-thestart button will be in: a depressedposition within the housing and a portion ofthe stop buttomwillproject beyondthe surface of the housinginposition to the moved inwardly tostop'theoperation of the press or machine. Whenithe stopJbutt'on is'pressed by the machine operator,iti willrmove inwardly to a recessed position withinftheihousing and the start buttonwill be automatically moved outwardly into apo'sition of readinessto be actuated to restart the pressor'machine.

It is an object of the present invention'itoiprovide'a simple and inexpensive safety: device which may be readily attached to the housing oftthe electricaleswitch to prevent theimovement ofthe' switch push buttons necessary tostart th'e operation of'the press or machine. The pre sent invention comprises a means forpreventin'gor blocking outward movement of the stop 'button when itris recessed within theswitchhousing;thestop buttonxbein'g in a recessedpositioniwlien themachine: is not operating. Because'ofitheimeansdnterlockingthe two buttons for correlatedmovement, when outward moVementofthe-stop:but-

tonis-prevented or blocked thest-art button cannot be moved inwardly to close the electrical circuit necessary to put the machine orpress in .operation. Inits illustrated embodiment, the-presentinvention comprises a coverplateadapted to befastened to the front faceoftthe:switch.housing and having a. plug portion .fastened .to the:

inner sidethereof, which plug. portion maybe inserted'iiito the cavity in the 'front ia'ce'ofthehousingwesilltingwhen: the stop button iszplaced in: its recessed-pr rma'chine inoperative position, and means beingiprovided to lock'. the coverplate to th-erswitch housing to prevent unauthorizedremoval of the safety: device, the cover plateiwhen iocked to the housing. efi'ectively blocking zany outward movement of the stop button and thereby blocking the inward movement of theistart button. Aszlong as the safetydevice isinblocking :position'the1machine cannot be operated. Thus, arepair man after having inserted the safety device inc-blocking position on the switch and. put the key thereto. in his pocket 1 may crawl intoathe machine or-apparatus. to make any necessary'repairswithout the danger of someonerinadvertently putting themachine or apparatus into operation while: he-is in.- a positionto be injured byiany of its moving parts.

Other features, objects and advantages of this inventionherein illustrated will appear in -the following description reference being had to the accompanying drawings forming a part of "the specification wherein like reference numerals designate corresponding parts in the several views.

Fig. 1: is a front elevation of a: start stop switch and illustrating the present invention mounted thereon.

Fig. 2-isa section taken substantially through line 2-2 of Fig. 1 looking in the direction of the arrows.

3 i isa section taken Substantially through line3- 3iof Fig 2-looking'in the direction of the,

arrow.

Fig 4 isan-explodedview showing the compo nent parts of thesafety device comprising the presentinvention.

Before explaining in detail the present inven-- tioniit is tobe understood that the invention is Also itwis to be. understood that the phraseology or terminology employed herein is for the'purposeof description andnotof limitation.

Referringv more-o particularly to the drawings, the electrical switch .to which the present invention isappliedcomprises, for illustrativepurposes, :a.metalcasing or housing 19 whichfits overhanrinner casing ll made of a dielectric ma terial. Theouterand inner casings lil and II, respectively, are adapted: to be-fastened by' means .of. screws I. 2 as aunit-to the frame structure [:3

of-astampingipress. machine or other --apparatus. alsuitablerubber insulating gasket 1 l i being. prosvi'ded to..insulate..the.metal casing is from the Two push buttons If! and are slidably mounted within the bores I? and I8 respectively. The push buttons I3 and 23 are provided with stems or extensions 19a and 20a respectively, which project through apertures 2| and 22 in the base plate 523 of the inner casing H, the apertures 2| and 22 being in alignment with the bores l1 and it in the outer casing Iii. A compression spring 23 is seated over each stem 19a, and 20a, each spring being adapted to be compressed between one surface of the base plate 23 and the inner surface of the corresponding push button I9 or 263.

Mounted on the end of each push button stem tea and 20a is a cylindrical brass member 25. Pivotally connected to one end of each link 25 is a dielectric link 26. Each link 26 is pivotally connected to one end of a cross bar 21 which is pivoted intermediate its ends on a pin 28 carried on one end of a yoke member 29 mounted at its other end to the base plate 23 of the inner casing H.

The foregoing construction and arrangement is such that when one push button is in a depressed position relative to the outer casing l0, as for example the push button 20 as shown in Fig. 2, the other push button will have a portion thereof projecting beyond the outer surface of the boss 6 of the outer casing l8. Movement of the outwardly projecting button in an inward direction automatically results in the cross bar 2? urging the recessed button outwardly into a position of readiness to be actuated when desired by the machine operator.

Suitable contact means in the form of metallic washers 30 are carried on each cylindrical brass member 25. The contact means are urged by compression springs 3| into contact with suitable contact elements 32 carried within the inner casing II.

It is believed that the foregoing description of the illustrative type of electric switch with which the present invention is adapted to be utilized is of sufficient detail for an understanding of the invention.

The embodiment of the invention herein illustrated comprises a cover plate generally designated 33 which comprises a flat section 34 substantially equal in area and similar in shape to the upper surface of the switch housing boss I6 and having a flange 35 extending from each longitudinal edge thereof, the depth of the flanges being substantially equal to the height of the housing boss is plus the distance that the push buttons project beyond the upper surface of the boss when in position to be actuated. A plug member 35 is welded or fastened to the inner side of the plate section 34. The plug 36 is located on the plate section in position to enter the cavity in the surface of the housing resulting from the stop button being in a recessed or machine inoperative position, as shown in Fig. 2. Thus, with the cover plate in place as shown in Figs. 1 and 2, it is impossible for any one to push the start button inwardly to close the electrical circuit necessary to place the press or machine in operation. Further, even if a tool were deliberately inserted between the cover plate 33 and. the outwardly projecting button 19 to actuate the start button despite the fact that the safety device was in place, the plug member 36 would blockthe outward movement of the button 20 necessary to permit the inward 'movement of the button l9.

4 the switch housing 10 in any suitable manner. As illustrated, the boss l6 of the switch housing [0 and the flanges 35 are provided with aligned holes 3? and 38 respectively through which a pin 39 is inserted to hold the cover plate 33 to the switch housing. The pin 39 is provided with an eye 40 and the cover plate 33 is provided with an apertured bracket 4| to which a small padlock 42 may be attached to lock the pin 39 to the cover plate 33 thereby to prevent unauthorized withdrawal of the pin 39.

When for any reason it is desired to prevent the operation of a press or machine, the safety device embodying the present invention is readily fastened to the switch housing with the plug member 35 inserted into the bore 16. With the padlock 42 in place the switch cannot be actuated to start the drive means for the press or machine. When it is desired to place the machine back in service, it is only necessary to open the padlock 42. pull the pin and remove the cover plate 33. The present invention therefore provides an effective and efiicient as well as inexpensive means of preventing unauthorized or inadvertent operation of a press or machine as when undergoing repairs.

I claim:

1. A safety device for use in conjunction with an electrical switch having push button actuating elements slidably mounted within recesses in an embossed portion of the switch housing, said push button elements being interlocked for correlated movements so that when one button is shifted inwardly into depressed position within one of said recesses another button is shifted outwardly into operative position, comprising a cover plate adapted to fit over the face of said embossed portion, a plug portion fastened to said cover plate and insertable into said one recess in position to block said one button when said plate is at the cover position, and means for releasably holding said cover plate suificiently immovably at the cover position to block actuation of said buttons.

2. A safety device for use in conjunction with an electrical switch having push button actuating elements slidably mounted within recesses in an embossed portion of the switch housing, said push button elements being interlocked for correlated movements so that when one button is shifted inwardly into depressed position within one of said recesses another button is shifted outwardly into operative position, comprising a cover plate adapted to fit at a cover position over the face of said embossed portion, said cover plate having flanges extending from two opposite edges thereof, a plug portion fastened to said cover plate and insertable into said one recess in position to block said one button when said plate is at the cover position, and means cooperable with said embossed portion and said flanges to hold said cover plate sufficiently immovably at said cover position to block actuation of said buttons.

3. A safety device for use in conjunction with an electrical switch having push button actuating elements slidably mounted within recesses in an embossed portion of the switch housing, said push button elements being interlocked for correlated movements so that when one button is shifted inwardly into depressed position within one of said recesses another button is shifted outwardly into operative position, comprising a cover plate adapted to fit at a cover position over the face of said embossed portion, said cover The cover plate 33 may he held in place on plate having substantially parallel flanges extending from two opposite edges thereof, a plug portion fastened to said cover plate and insertable into said one recess in position to block said one button when said plate is at the cover position, said flanges and said embossed portion intermediate said buttons having holes therein aligned when said plate is at the cover position, and pin means inserted through said holes to hold said cover plate on said housing thereby to hold said plug portion in said one recess and block outward movement of said one button thereby preventing actuation of the other button.

4. A safety device for an electrical switch comprising a support, start and stop push buttons interconnected for shiftable movement in unison and in opposite directions, the stop button being shiftable inwardly within a recess in the support whereby the start button will be shifted outwardly into operative position, said device compris ing a cover plate adapted to fit at a cover position over the face of the support, a blocking means fastened to said cover plate and insertable into said recess into blocking position with respect to said stop push button when said plate is at the cover position, and locking means for holding said cover plate sufficiently immobile to block actuation of said buttons.

5. A safety device for an electrical switch comprising a support, start and stop push buttons interconnected for shiftable movement in unison and in opposite directions, the stop button being shiftable inwardly within a recess in the support whereby the start button will be shifted outwardly into operative position, said device comprising a cover plate adapted to fit at a cover position over the face of the support, a blocking means fastened to said cover plate and insertable into said recess into blocking position with respect to said stop push button when said plate is at the cover position, said support having keeper means intermediate said buttons, said cover plate having apertures therein adapted to be placed in alignment with said keeper means when said plate is at the cover position, and pin means insertable through the apertures in said cover plate cooperable with said keeper means to fasten said cover plate to said support to hold said blocking member in position within said recess.

6. In a safety device for use in conjunction with an electrical switch having push button actuating elements slidably mounted within recesses in a housing and interlocked for correlated movements so that when one button is shifted inwardly into depressed position within one of said recesses another button is shifted outwardly into operative position, means to block outward movement of one of said buttons from its depressed position within its recess comprising a cover plate adapted to fit over said buttons at a blocking position and having a plug portion insertable into the latter recess at the blocking position, and means for releasably holding the cover plate at the blocking position.

'7. In a safety device for an electrical switch mounted in a housing and having start and stop push buttons coupled to move in unison and in opposite directions so that when either button is moved inward to a depressed position with respect to said housing the other button is moved outward to an extended position, the combination of fixed supporting means having recesses into which said buttons are shiftable, means to block outward movement of one of said buttons depressed within its recess comprising a cover member having a plug portion insertable into the latter recess in blocking position with respect to the button depressed therein, and means for releasably locking said cover member at the block ing position.

8. In a safety device for an electrical switch mounted in a housing and having start and stop push buttons coupled to move in unison and in opposite directions so that when either button is moved inward to a, depressed position with respect to said housing the other button is moved outward to an extended position, the combination of fixed supporting means having recesses into which said buttons are shiftable, means to block outward movement of one of said buttons depressed within its recess comprising a cover member having a plug portion insertable into the latter recess in blocking position with respect to the button depressed therein, said cover member at the blocking position also having portions adapted to fit over said buttons, and means for releasably locking said cover member at the blocking position.

9. In a safety device for an electrical switch mounted in a housing and having start and stop push buttons coupled to move in unison and in opposite directions so that when either button is moved inward to a depressed position with respect to said housing the other button is moved outward to an extended position, the combination of fixed supporting means having recesses into which said buttons are shiftable, means to block outward movement of the stop button from its depressed position within its recess comprising a cover plate having a plug portion insertable into the latter recess in blocking position with respect to the stop button, said plate at the blocking position being adapted to cover said buttons, and means for securing said plate at the blocking position.

19. In a safety device for an electrical switch mounted in a housing and having start and stop push buttons coupled to move in unison and in opposite directions so that when either button is moved inward to a depressed position with respect to said housing the other button is moved outward to an extended position, the combination of fixed supporting means having recesses into which said buttons are shiftable, means to block outward movement of the stop button from its depressed position within its recess comprising a cover plate having a plug portion insertable into the latter recess in blocking position with respect to the stop button, said plate at the blocking position being adapted to cover said buttons, said supporting means having a portion interme diate said buttons, a pinhole extending in said latter portion transversely of the axes of shifting of said buttons, said cover plate having lateral flanges at opposite edges thereof, said flanges having pinholes therein adapted to align with the pinholes in said supporting means when the cover is at the blocking position, and pin means extending through said holes to hold said plate at the blocking position, said flanges abutting said supporting means to block pivoting of said cover plate about the axis of said pin means.

EDWARD R. MCIQTRICK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,706,518 Blough Mar. 26, 1929 1,762,371 Wilhelm June 10, 1930 2,484,424 Rosing Oct. 11, 1949 

